Remove outdated info about yanked crates (RustPython#5111)

The `rustpython-*` crates have been published since this message was added.

Author: olivierlemasle

README.md

@@ -62,10 +62,6 @@ Welcome to the magnificent Rust Python interpreter
 >>>>>
 ```
 
-(The `rustpython-*` crates are currently yanked from crates.io due to being out
-of date and not building on newer rust versions; we hope to release a new
-version Soon™)
-
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